Clarification of the genus Nematothallus Lang

Upper Silurian and lowermost Devonian fossil plant assemblages are often dominated by fragmentary remains of problematic land plants that are composed of a tubular anatomy. Traditionally, these remains have been divided into two morphotypes: large three-dimensionally preserved axes (the Prototaxites group), and smaller thalloid incrustations referred to the genus Nematothallus Lang. Because of their peculiar anatomy of different combinations of tubular elements, these plants do not appear to be closely related to the Tracheidatae (sensu Bremer et al., 1987). Neither do they fit easily into any extant algal groups (Rossat, 1952; Edwards, 1982; Strother, 1988). For these reasons, when he first described the genus Nematothallus, Lang (1937) constructed an informal class of plants, the nematophytales, to include these fossils. Strother (1988) further emphasized the differences between the nematophytales and both embryophytes and algae by placing them into a new group, the Paraphyta.